From 15,000 feet to 20,000 feet, how many packs can the APU operate?

The A320's Auxiliary Power Unit (APU) is designed to provide pneumatic (bleed air) power to support the aircraft systems, including cabin conditioning, at various altitudes. From 15,000 feet to 20,000 feet, the APU can efficiently operate only one pack. This limitation is primarily due to the decrease in performance and capacity of the APU at higher elevations where the air density is lower, which impacts its efficiency in supplying the necessary bleed air.

When flying at these altitudes, the APU is still capable of providing the required pneumatic supply for one pack, ensuring that the cabin remains pressurized and comfortable for passengers. Operating more than one pack simultaneously in this altitude range would exceed the APU's capability to provide sufficient bleed air, which could lead to operational issues and insufficient environmental control within the aircraft.

Understanding this limitation helps ensure the A320 operates within its specified parameters, ultimately maintaining safety and efficiency during flight operations.